Identical Toilets With Water Levels of Different Heights

We have identical 3.5 gallon Kohler toilets (same model #s) that we purchased twenty years ago. Both have Fluidmaster 400A fill valves that are set as low as the screw mechanism allows. I've noticed (after complaints from my wife) that the water level in one toilet is 3/4" higher than it is in the other toilet. No adjustment I do will lower the water level in the higher one. Can anyone explain why?

On another thread in this forum, someone suggests switching to a padded seat. I suppose that would work, but I don't understand why we have this difference.

Water level in the bowl is determined by the top of trapway bend. It can't be higher than that. You can slowly pour water in the bowl and then mark it at it's highest level.
If the bowl refill from the tank does not match that, check to make sure that the refill tube from the fill valve is pointed down the overflow tube. It should daylight above the overflow or it will siphon the tank.

Thanks for replying. The problem isn't that we're losing water. The water level is too high in one toilet. For years, it wasn't a problem. Then the level changed in one, but not the other. I just don't understand how the same Kohler toilets with the same fill valve set at the same height results in water 3/4" higher in one of them. The refill tubes in both are pointed into the overflow tube, but not touching the water in the tube.

Also, the poster seems to be saying that there is now "too much" water accumulating in one bowl on refill, not that there is too little in the other. This seems odd, because any "extra" water is going to flow over the weir and down the drain; it would be odd for buildup to raise that bend.

Almost makes me wonder if both toilets had long been underfilled, and now one is filing to the right level. Easy way to tell is to pour a few cups of water slowly into both until they start draining, and let them drain slowly until they settle. Then see if they aren't at the same height.

Most people, of course, don't complain about a water spot being too big. It's usually something that people like.

Ultimately, of course, if one wants to lower the water level in the toilet (which doesn't seem adviseable but you can do it), you can just install a Korky 528MP (or MPK at Lowe's) MaxPerformance fill valve with the silver top, costing about $11, and adjust the refill level to your liking with its little valve on the refill tube.

Because modern toilets are required to use a fairly small amount of water, there's no excess in the scheme. So, it is designed to have the bowl full when you start a flush cycle. If it isn't, it's possible that it either won't flush at all, or not clear the bowl. This leads to it working poorly on the first try, and because it doesn't have enough to generate a good siphon to empty it, there's enough (dirty) water left when you try it again.

I don't really get the point about the refill needing to be right at the max bowl level. If you fill a bucket full of water to the top and put your hand into it, what happens? It overflows, correct? A bowl that it at max level will overflow into the trapway when enough liquids or more so with solids are added.

Ok, check the flapper if it is letting out to much water that will cause more water to be in the bowl, simply adjust it could also be the float if the runs a few seconds longer that it should will result in high water levels. you may also try to replace the kit all together.

I don't really get the point about the refill needing to be right at the max bowl level. If you fill a bucket full of water to the top and put your hand into it, what happens? It overflows, correct? A bowl that it at max level will overflow into the trapway when enough liquids or more so with solids are added.

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The point being, the toilet bowl needs to be full when you flush it, or it typically underperforms. IOW, it's best to start out with it filled to the brim (the top of the weir determines how full it can be), then, regardless of how much or little gets added, it should have the same flushing efficiency. On a severely underfilled bowl, that may not happen as it may not get enough added to raise it to the 'full' level, resulting in a weak flush, if it flushes at all (worst case).